Labile Emotions Adolescents can shift moods rapidly, vacillating between happiness and sadness, self-confidence and worry. Some of these mood changes are caused by biological sources. Moreover, complex social interactions such as conflicts with friends, school pressures and experimentation with romantic relationships can exacerbate the labile emotional state of adolescents.
Peer Relationships
BULLYING
PROBLEMS WITH THEIR PARENTS
Teens are always rebel and argumentative with their parents because they need to find their identity. Moreover, they need more privacy, so when they are at home they tend to stay in their own rooms by themselves...
... or at the phone with their friends for hours!
From : http://thetravellingteachers.blogspot.it/search/label/adolescence